1.

यदि `secA+tanA=a,` हो तो `cosA` का मान होगा ?A. `(a^(2)+1)/(2a)`B. `(2a)/(a^(2)+1)`C. `(a^(2)-1)/(2a)`D. `(2a)/(a^(2)-1)`

Answer» Correct Answer - b
`SecA+tanA=a`
we know that
`sec^(2)A-tan^(2)A=1`
`(secA-tanA)(secA+tanA)=1`
`(secA-tanA)alpha=1`
`secA-tanA=(1)/(alpha)`
`secA+tanA=alpha`
`2secA=alpha+(1)/(alpha)`
` 2sec(1)/(A)=(a^(2)+1)/(alpha)`
`sec theta=(alpha^(@)+1)/(2alpha)`
so, `cos theta=(2alpha)/(a^(2)+1)`


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